text: The reaction can be demonstrated by starting with solutions of potassium cyanate and ammonium chloride which are mixed, heated and cooled again. An additional proof of the chemical transformation is obtained by adding a solution of oxalic acid which forms urea oxalate as a white precipitate.
  Alternatively the reaction can be carried out with lead cyanate and ammonia. The actual reaction taking place is a double displacement reaction to form ammonium cyanate:
  Ammonium cyanate decomposes to ammonia and cyanic acid which in turn react to produce urea:
  Complexation with oxalic acid drives this chemical equilibrium to completion.